Changes in size and shape of the cells of the retinal pigment epitheium (RPE) of the chick embryo are followed as a function of the expansion in area of the RPE which occurs during the development and growth of the eye. Strips of eye wall are cut from embryos of different ages along known ocular meridians, mounted on microscope slides, transilluminated, and photographed through a compound microscope. Such photographs, calibrated for magnification, not only reveal the three-rayed net formed by appositions of RPE cells, but also permit quantitative study of cell size, shape (sidedness) and nuclearity as functions of position within the eye and of developmental time. Thus far, it has been ascertained that: 1) RPE cells increase in surface area and in volume as a function of age; 2) this expansion is more marked in the fundus of the eye than toward the ora serrata; 3) RPE cells undergo this expansion in response to tensions generated by the expanding vitreous body; 4) a small percentage of cells is binucleate, larger in area than uninucleate neighbors, tends to have more sides than uninucleate cells, and occurs more commonly at the fundus.